Synchronizing system



Dec, 31, 1940.

SIGNAL INPUT RECORD/N6 AMPLIFIER 7'0 RECORDER RECORD/Nb AMPL I Fl ERSIGNAL nvpur 70 RECORDER J. N. WHITAKER SYNCHRONIZING SYSTEM Filed Oct.8, 1938 2 Sheets-Sheet I l OSCIUATOR AMPLIFIER fizz 2f GNET/cc'oMMumrolz osc/uA TOR AMPLIFIER gig E f DRIVE MOTOR RECORD/N6 SPIRALRECORD/N6 AMRL lF/ER SIGNAL 5! INPUT W 7'0 RECURDER use/1mm AMPLIFIER 55J 64 \SYNC/IRONOUS MOTOR 23 RECORD/(V6 SPIRAL 47 66 49 45 COMMUTA O 43INVENTOR. JAMES WHITAKER A TTORNEY.

Patented Dec. 31, 1940 UNITED STATES SYNCHRONIZING SYSTEM James N.Whitaker, Tuckahoe, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application October 8, 1938, Serial No. 233,927

16 Claims.

This inventior n slates to synchronizing and automatic framing methodsand apparatus, and more particularly, to synchronizing and automaticframing methods and apparatusapplicable to facsimile and televisionsystems in which the speed of the recording mechanism is controlled byreceived signals supplied to a local oscillator during time intervalsdetermined by the speed of the recording mechanism.

My new method and apparatus for accomplishing synchronization has thebeneficial eflect of not only providing accurate synchronizing with aminimum of apparatus, but also provides at the same time automaticframing of the received image so that the entire installation is furthersimplified by eliminating the necessity for providing framing apparatus.

A further feature of my invention is the fact that the received signalsfor synchronizing are 20 derived directly from the signalsrepresentative of the image or message transmitted.

In accordance with my invention, a portion of the received signals isfed through a commutator to a local oscillator. The local oscillatorsupplies the synchronizing power either in part or in whole to therecording mechanism. The commu-v tator through which the receivedsignals are fed to the local oscillator, is controlled by the recordingmechanism, and the commutator is so arranged that the received signalsare fed to the oscillator during time intervals when the frequencydeviates from that frequency necessary to maintain the apparatus insynchronism. It will thus be appreciated that my invention diil'ers fromknown synchronizing methods in the use of a commutator whose speed isdetermined by the speed of the recording mechanism and in which a localoscillator supplying the synchronizing en- 40 ergy has its frequencycontrolled by the commutator acting in conjunction with receivedsignals. By suitably selecting the number of segments on the commutatorwith regard to the speed of the recording mechanism, it is possible toprovide at the same time automatic framing or phasing of the receivedrecord.

Accordingly, it is one of the objects of my in- 'vention to provide animproved synchronizing method and apparatus for facsimile and televlsionsystems.

Another object of my invention is to provide an improved synchronizingmethod and apparatus together with automatic framing for facsimile andtelevision systems.

A further oiject of my invention is to provide a synchronizing systemfor facsimile and television apparatus in which the synchronizingsignals are derived from the signals representative of the image tocontrol a local oscillator for regulating the speed of the receivingequipment by using a commutator whose speed is controlled by the localsource of oscillations and at the same time to restrict theefiectiveness of the incoming signals to control the frequency of theoscillator so as to provide correct phasing or framing of the receivedimage.

Other objects of my invention will become clear to those skilled in theart upon a reading of the following detailed desecription taken togetherwith the drawings. 1

In the drawings, Fig. 1 shows in block diagram one embodiment-of myinvention showing schematically the use of energy derived from receivedsignals to control the local oscillator through a commutator; so

Fig. 2 shows in block diagram form a modification oil the form of theinvention shown in Fig, 1, in which a shorting bar commutator replacesthe magnetic commutator shown in Fig. 1;

Fig. 3 shows a further embodiment of my invention in a modified form ofboth Figs. 1 and 2, in which a synchronous motor replaces the phonicwheel shown in Figs. 1 and 2; while Fig. 4 shows in schematic diagram inmore detail, the electrical circuits associated with the synchronousmotor and commutator shown in Fig. 3.

In describing my invention, for convenience it will be assumed that theinvention is to be used in'connectlon with tape facsimile systems. Insuch a system, the transmitter may be of the type shown and disclosed inthe application of G. L. Dimmick, entitled Scanning device, which wasfiled September 21, 1937, and bears application 0 Serial Number 164,847.In such a scanner the essential components comprise a motor, a tape feedmechanism upon which the message to be transmitted is transcribed, asource of light, an optical system, means for moving the light beam 5across the tape, and a photoelectric cell with its associated amplifiersystem. The drive motor may be of the synchronous cycle per second type.The tape feed system comprises a sufflcient number of rollers and guidesto draw the tape '39 past the scanning point at a constant speed. Thelight source, which may conveniently be a prefocused projection electriclamp, has interposed between it and the tape an optical system forproducing a sharply focused beam of light of small area upon the tape.interposed between the optical system and the tape there is provided,for example, a rotating polygonal prism to cause the beam of light tosweep across the tape in a direction perpendicular to the motion of thetape. Alternatively, there may be provided a scanning disk having anumber of small apertures spaced equi-distaint around the periphery ofthe disk and at equal radial distances from the center of the disk. Thereflected light from the tape is projected upon the photoelectric cellso as to convert the varying quantity of refiected light into electricalsignals of varying amplitude. A suitableamplifier amplifies the producedelectrical signals and the output of the amplifier may then be used tosuitably modulate a transmitter or the output may be impressed upon atransmission line.

It will be appreciated that during the scanning process, since thescanning takes place at a predetermined rate, the generated electricalsignals produced by the conversion of light will produce signalcomponents of a frequency which bear a fixed relation to the scanningfrequency or rate, in addition to those signals having frequencycomponents related to the varying density of the scanned record. Thisfact is well known in the art and is treated in considerable detail inthe paper by Mertz and Gray, entitled A theory of scanning and itsrelation to the characteristics of transmission signals intelephotography and Turning now to Fig. 1, the transmitted signals areimpressed after suitable detection andamplification, if necessary, uponthe recording amplifier I3. The output of the recording amplifier I3 maybe conveniently in the form of push-pull signals and fed to the recorderfrom the terminals 3|. The recorder may conveniently take the form ofthat shown in United States Patent No. 2,104,109 to C. J. Young forApparatus for facsimile recording, issued January 4, 1938. The output ofthe recording amplifier I3 is also fed to an oscillator I5 through amagnetic commutator comprising the core having an air gap, and windings21 and 29. The recording spiral 23 of the recorder is of such dimensionsand so positioned as to lie within a portion of the air gap of the core25. It will be appreciated, of course, that the recording spiral 23 ismounted on the shaft 22 of the drive motor 2I so that the recordingspiral during rotation varies the reluctance of the magnetic path byinterposing more or less magnetic material during its rotation. It willbe appreciated that the recording spiral made of magnetic material, suchas hardened steel for example, during the interval when the spiralridges lie parallel to the plane of the core, shortens the air gap andprovides a maximum magnetic material path, while during the intervalswhere the spirals are substantially perpendicular to the plane of thecore, the air gap has been lengthened while the magnetic material pathhas been decreased under which contransmission, issued December 10,1929. much as the oscillator I5 is to have its frequency ditions maximumreluctance of the path is provided.

- It will thus be appreciated that during the rotation of the spiral,the voltage transferred from the winding 21 to the winding 29 will varyin accordance with the reluctance of the path of the core 25, so thatthe intensity of the signals fed to the oscillator I5 will likewise varyin accordance with the rotation of the spiral. The oscillator I5 has itsoutput fed to an amplifier II whose output in turn is fed to a phonicwheel I9 mounted on a shaft 20 of the drive motor 2I. It will thus beseen that the alternating current fed to the phonic wheel I9, which ineffect acts as a synchronous motor, will control the speed of the drivemotor 2| at a rate determined by the frequency of the oscillator I5. Theuse of a phonic wheel for this purpose, is, of course, well known in theart, as typified for example by the United States Patent No. 1,738,673to Schroter, for Synchronizing arrangement for picture Inascontrolled bythe received signals impressed on the signal input II, it is necessaryto provide an oscillator having fair frequency stability whosefrequency, however, is capable of being controlled by injecting duringperiodic intervals a small amount of controlled energy. An oscillatorsuitable for this purpose may conveniently take the form of a dynatronoscillator of the type disclosed in United States Patent No.2,067,366,issued to James N. Whitaker, January 12, 1937, for Dynatronoscillator circuit.

In operation, the received signals impressed on the signal input andpassed through the magnetic commutator to the dynatron oscillator willhave their intensity controlled, of course, by the position of therecording spiral 23 at the moment during which signals are actuallybeing received. Since'the position of the recording spiral is determinedby the speed of the drive motor, which in turn is controlled through thephonic wheel by the oscillator, it will be readily appreciated that ifthe drive motor is running at a speed different from that of the motorof the transmitting equipment, the spiral has such a position as to giveminimum reluctance of the path, so that a. relatively strong signal ispassed through the magnetic commutator to the oscillator to shift itsfrequency in such a direction as to put the speed of the phonic wheeland drive motor in synchronism with the transmittingmotor. If the drivemotor is running at synchronous speed, then the recording spiral is insuch a position as to provide maximum reluctance so that the receivedsignals, being greatly attenuated due to the increased reluctance, areineffective to change the oscillator frequency.

During the scanning of the tape at the transmitter at the moment whenthe scanning of one line is completed and the scanning of the followingline is about to commence, there is produced a marginal impulse. If themarginal impulse is received at the time when the spiral tooth is in aposition to provide minimum reluctance, and hence maximum transfer ofenergy, the dynatroti oscillators frequency will be synchronized withthe impulse. Inasmuch as the marginal impulse Occurs at the end of eachline, it will be appreciated that framing likewise takes place of thereceiving equipment.

While this method and apparatus afl'ords ex cellent synchronizing andframing, it will be appreciated that the design of the magneticcommutator together with the necessity for positioning the commutator inclose proximity to the recording spiral makes it desirable to simplifythe commutation apparatus. Accordingly, an improved form of my inventionis shown in Fig. 2, in which the magnetic commutator is replaced by amore conventional type of shorting bar commutator mounted on the shaftof the drive motor.

Turning to Fig. 2, it will be noted that mounted on the shaft 22 of thedrive motor is the shorting bar commutator 43 comprising a hub ofinsulating material such as Bakelite, for example, imbedded in whichthere is a plurality of metallic conducting segments 45-45 which maytake the form of copper bars, mounted on the periphery equi-distant fromeach other and parallel to the axis of the commutator. A pair of brushes4! and 49 bear across each segment or shorting bar in succession as thecommutator is rotated. Signals from a recording amplifier I3 arecapacitatively coupled through the condenser 5| to the oscillator I5through the brushes 41 and 49 and the commutator 43. Thus, for example,when one of the segments 45 is in contact with the brushes 41 and 49,any signals present in the output of the amplifier I3 will be passed tothe oscillator I5. When the copper segment bars 45 are not in contactwith the brushes 4! and 49, the circuit between the recording amplifierI3 and the oscillator I5 is open, so that no signals can be passed tothe oscil- .lator. In other respects the synchronizing equipment andmethod of operation is identical with that described above in connectionwith Fig. 1. Under these conditions, it will be appreciated that thesynchronizing and framing is improved over that of the system showninFig. 1 in view of the fact that a much better differentiation inamplitude between the periods during which signals are fedto theoscillator and those periods during which no signals are fed to theoscillator is provided by the shorting bar commutator than by themagnetic type commutator.

As an alternative form of synchronizingthe modification of my inventionshown in Fig. 2 may substitute a synchronous motor for the drive motorand phonic wheel combination, as shown in Fig. 3. In this modification,instead of merely supplying synchronizing power to the phonic wheelwhile the bulk of the drive power is supplied by a drive motor havinginherently poor speed regulation, the output of the oscillator I5 isamplified to a greater extent by the amplifier 63 and the output feddirectly to the synchronous motor 65. Under these conditions thesynchronous motor will, of course, maintain a speed which is determineduniquely by the dynatron oscillator I5 and as is well known in the art,its speed is determined at all times by the frequency of the dynatronoscillator. This arrangement has the beneficial effect of overcominghunting which may be present in the phonic-wheel-drive motor type ofsynchronizing system. It is in this case, of course, that the ampilfier63 is called upon erally preferred to the form of synchronizing shown inFigs. 1 and 2 for example. 'In all other respects, however, themodification shown'in Fig. 3 is substantially identical with that shownin Fig. 2.

In Fig. 4 I have shown in detail schematically the apparatus shown inblock diagram form in nents. In the drawing VT1 together with itsassociated components comprises the first stage of an amplifier foramplifying the received signals impressed on the signal input. It willbe recognized that this is a conventional type of transformer coupledinput with potentiometer control 7 for regulating theintensity of theincoming sig nals at P1. The tube is self-biased by theresistor-capacitor combination R101. The output, after being amplified,is fed through the transformer T2 to the diode-triode VT: which performsfour functions. In the first place, the two diodes act as a full waverectifier for the amplified signal. Secondly, the triode portion of thistype acts as a limiter by providing suitable values of R2 and C2 acrosswhich the rectified signal voltage is impressed. The output of VT2 isused to operate the marking tube VTs and a portion of the output is alsoused to operate the reversing tube VTa. The reversing tube VT; operatesthe spacing tube VT4 of the push-pull drive amplifier and the outputs ofthe tube W4 and VT5 operate the facsimile recording head by driving theprinter bar II against the recording spiral 23. It will be noted that aportion of the output of the tube VT5 is fed through the capacitor C3and commutator 43 to the grid input circuit of the tube VTs. The tubeVTs is a dynatron oscillator and there is provided a potentiometer P2 inits control circuit so as to regulate the amplitude of the energy fedthrough the condenser C3 and the commutator 43 to control the frequencyof the dynatron oscillator. It will be appreciated, of course, that thefrequency of the dynatron oscillator in this arrangement is determinedby the magnitude of the biasing voltage provided by the resistor R13 andcondenser C4, as well as the superimposed voltage derived from theoutput of the tube VTs. The marginal impulses which serve to control thefrequency of the dynatron oscillator also, as pointed out above, serveas framing signals. In this connection, it is, of course, important tonote that the number of segments or shorting bars 45 on the commutator43 must bear a predetermined relation to the number of entries of therecording spiral. Thus if a single entry spiral is used, the commutatorwould only have one short circuiting bar. If a six entry spiral is used,six short-circuiting bars are recorded, assuming that both the spiraland commutator are operated at the same shaft speed. If it should bedesirable from the standpoint of mechanical design to operate the spiraland commutator at different shaft speeds, the

The output of the second stage of the amplifier We is then utilized todrive a push-pull stage We and V'I'm and the .sizeof the tubes are sochosen as to deliver approximately or watts of energy for feeding thesynchronous motor 65 which may have a rating of %oo horse power, forexample.

From a consideration of Fig. 4 and its description, it is to be notedthat the synchronizing system provided is one of extreme simplicity,since the only additional mechanical equipment is the commutator 43which can, of course, conveniently be mounted on the motor shaft and therelatively simple electronic circuit comprising the dynatron oscillatorWe and the amplifier comprising the tubes VT: through VTm. Yet, it willbe appreciated that even though the circuit arrangement and apparatus isof extreme simplicity, this system is capable of maintaining faithfulsynchronizing and at the same time providing the very desirable featureof automatic framing.

Having described my invention, what I claim is:

1. The method of synchronizing recording apparatus which comprises thesteps of providing a local source of wave energy, controlling the speedof the recording apparatus from the source of wave energy, receivingremotely generated image recording signals, amplifying the receivedsignals, deriving wave energy from the amplified received signals,feeding the derived energy to the local source of wave energy to controlthe frequency of the wave energy from the source, and controlling thetime duration during which the derived energy is effective to controlthe frequency of the local source of wave energy in accordance with thespeed of the recording apparatus.

2. The methodof synchronizing recording apparatus which comprises thesteps of providing a local source of wave energy, driving the recordingapparatus from the source of wave energy, receiving remotely generatedimage recording signals, amplifying the received signals, deriving waveenergy from the amplified received signals, feeding the derived energyto the source of wave energy to control the frequency of the wave energyfrom the source, and controlling the time duration during which thederived energy is effective to control the frequency of the source ofwave energy in accordance with the speed of the recording apparatus.

3. The method of synchronizing a rotating motor which comprises thesteps of providing a local source of wave energy, controlling the speedof said motor from thesource of, wave energy, receiving remotelygenerated image recording signals, amplifying the received signals,deriving wave energy from the amplified received signals, periodicallyfeeding the derived energy to the source of wave energy to control thefrequency of the wave energy from the source, and controlling theperiodicity at which the derived energy is effective to control thefrequency of the source of wave energy in accordance with 1 the speed ofsaid motor.

4. The method of synchronizing recording ap-- paratus which comprisesthe steps of providing a local source of wave energy, controlling thespeed of the recording apparatus from the source of wave energy,receiving remotely generated image recording signals, amplifying thereceived signals, deriving wave energy from the amplified receivedsignals, and feeding the derived energy to the source of wave energy tocontrol the frequency of the wave energy from the source whenever thespeed of the recording apparatus deviates from a predetermined value.

, 5. The method of synchronizing a rotating motor which comprises thesteps of providing a local source of wave energy. controlling the speedof the motor from the source of wave energy, receiving remotelygenerated image recording signals, amplifying the received signals,deriving wave energy from the amplified received signals, feeding thederived energy to the source of wave energy to control the frequency ofthe wave energy from the source whenever the speed of the motor deviatesfrom a predetermined value.

6. Synchronizing apparatus comprising a local source of wave energy,'means for controlling the speed of recording apparatus from the sourceof wave energy. means for receiving remotely generated image recordingsignals, means for amplifying the received signals, means for derivingwave energy from the amplified received signals, means for feeding thederived energy to the source of wave energy to control the frequency ofthe wave energy from the source, and means for controlling the timeduration during which the derived energy is effective to control thefrequency of the source of wave energy in accordance with the speed ofthe recording apparatus.

'7. Synchronizing apparatus comprising a local source of wave energy,means for driving recording apparatus from the source of wave energy,means for receiving remotely generated image recording signals, meansfor amplifying the received signals, means for deriving wave energy fromthe amplified received signals, means for feeding the derived energy tothe source of wave energy to control the frequency of the wave energyfrom the source, and means for controlling the time duration duringwhich the derived energy is effective to control the frequency of thesource of wave energy in accordance with the speed of the recordingapparatus.

8. Synchronizing system comprising a rotating motor, a local source ofwave energy, means for controlling the speed of said motor from thesource of wave energy, means for receiving remotely generated imagerecording signals, means for amplifying the received signals, means forderiving wave energy from the amplified received signals, means forperiodically feeding the derived energy to the source of wave energy tocontrol the frequency of the wave energy from the source, and means forcontrolling the periodicity at which the derived energy is effective tocontrol the frequency of the source of wave energy in accordance withthe speed of said motor 9. Synchronizing apparatus comprising imagerecording apparatus, a local source of wave energy, means forcontrolling the speed of the recording apparatus from the source of waveenergy, means for receiving remotely generated image recording signals,means for amplifying the received signals, means for deriving waveenergy from the amplified received signals, and means for feeding thederived energy to the source of wave energy to control the frequency ofthe wave energy from the source whenever the speed of the recordingapparatus deviates from a predetermined value.

10. Synchronizing apparatus comprising a rotating motor, a.1ocal.,source of wave energy, means for controlling the speed of themotor from the source of,wave energy, means for receiving remotelygenerated image recording signals, means for amplifying the receivedsignals, means for deriving wave energy from the amplified receivedsignals, means for feeding the derived energy to the source of waveenergy to control the frequency of, the wave energy from the sourcewhenever the speed of the motor deviates from a predetermined value.

11. In combination, an alternating current oscillator, means to amplifyenergy from the oscillator, a motor, means to control the speed of themotor from the amplifying means, a commutator driven by the motor, meansto receive picture recording signals, and means to feed a portion of thereceived recording signals to the oscillator through said commutator,whereby the oscillator is controlled by the received energy inaccordance with deviation of the motor speed from a predetermined valueof speed.

12. In combination, an alternating current oscillator, an amplifier foramplifying wave energy from the oscillator, a motor, a phonic wheelconnected to said motor, means to feed energy from the amplifier to thephonic wheel, a commutator driven by said motor, an image recordingamplifier, means to feed remotely generated image signals to saidamplifier, and means to feed energy from the recording amplifier to theoscillator through the commutator.

13. In combination, an alternating currentoscillator, an amplifier foramplifying wave energy from the oscillator, a motor, a phonic wheelconnected to said motor, means to feed energy from vthe amplifier to thephonic wheel, a magnetic commutator driven by said motor, a recordingamplifier, and means to feed energy from the recording amplifier to theoscillator through the magnetic commutator.

14 In combination, an oscillator supplying wave energy, an amplifier foramplifying wave energy from the oscillator, a synchronous motor, meansto drive the synchronous motor by energy from the amplifier, acommutator driven by the synchronous motor, a. receiving amplifier,means to supply signals representative of an object to be reproduced tothe receiving amplifier, and means to supply a portion of the amplified,re-

, ceived signals to the oscillator through the com- 'mutator.

15. In combination, an oscillator supplying wave energy, an amplifierfor amplifying wave energy from the oscillator, a synchronous motor,means to drive the synchronous motor by energy from the amplifier, acommutator driven by the synchronous motor, a receiving amplifier, meansto supply signals representative of an object to portion of theamplified received signals to the oscillator through the commutator.

JAMES WHITAKER.

